According to the state of the art, automatic transmissions, particularly for motor vehicles, comprise planetary gearsets, which are shifted using friction and/or control elements, such as clutches and brakes, and which are typically connected to a starting element that is subject to a slip effect and optionally provided with a lock-up clutch, for example a hydrodynamic torque converter or a fluid clutch.
A transmission of this type is described in EP 0 434 525 A1. It substantially comprises one input shaft and one output shaft, which are disposed parallel to each other, a double planetary gearset concentric with the output shaft and five control elements in the form of three clutches and two brakes, the selective operation of which, in pairs, determines the different gear ratios between the input shaft and output shaft. This transmission has a front-mounted gearset and two power paths, so that six forward gears are obtained by selective engagement in pairs of the five control elements.
In the first power path, two clutches are required for transmitting the torque from the front-mounted gearset to two elements of the double planetary gearset. These elements are substantially provided in the direction of power flow behind the front-mounted gearset in the direction of the double planetary gearset. In the second power path, a further clutch is provided, which detachably connects this path with a further element of the double planetary gearset. The clutches are arranged such that the inner disk carrier forms the output end.
Furthermore, from the published prior art U.S. Pat. No. 6,139,463 a compact multi-speed transmission in planetary design, particularly for a motor vehicle is known, which has two planetary gearsets and one front-mounted gearset as well as three clutches and two brakes. In this known multi-speed transmission, two clutches C-1 and C-3 are provided in a first power path for transmitting the torque from the front-mounted gearset to the two planetary gearsets. The outer disk carrier and/or the cylinder or piston and pressure compensation sides of the clutch C-3 are connected to a first brake B-1. Furthermore, the inner disk carrier of the third clutch C-3 is connected to the cylinder and/or piston and pressure compensation sides of the first clutch C-1. The inner disk carrier of the first clutch C-1 is arranged on the output side and connected to a sun gear of the third planetary gearset.
From DE 199 49 507 A1 by the Applicant, a multi-speed transmission is also known, of which on the drive shaft two non-shiftable, front-mounted gearsets are provided, which on the output side generate two rotational speeds. In addition to the rotational speed of the input shaft, it selectively switched by closing the control elements to a shiftable double planetary gearset acting upon the output shaft such that, for changing from one gear to the next higher or lower gear of the two actuated control elements, only one control element must be engaged or disengaged.
DE 199 12 480 A1 discloses an automatically shiftable motor vehicle transmission with three spider-mounted planetary gearsets as well as three brakes and two clutches for switching between six forward gears and one reverse gear and with one drive shaft and one output shaft. The automatically shiftable motor vehicle transmission is configured such that the drive shaft is directly connected to the sun gear of the second planetary gearset and that the drive shaft can be connected via the first clutch to the sun gear of the first planetary gearset and/or via the second clutch to the spider of the first planetary gearset. Additionally or alternatively, the sun gear of the first planetary gearset can be connected via the first brake to the transmission housing and/or the spider of the first planetary gearset can be connected via the second brake to the housing and/or to the sun gear of the third planetary gearset, via the third brake.
DE 102 13 820 A1 discloses a multi-speed automatic transmission, comprising a first input path T1 of a first speed ratio, an input path T2, which has a larger speed ratio than the input path T1; a planetary gearset of four elements, wherein the four elements are a first element, a second element, a third element and a fourth element following an order of elements on a speed diagram; a clutch C-2 transmitting a rotation from the input path T2 to the first element S3; a clutch C-1 transmitting the rotation from the input path T2 to the fourth element S2; a clutch C-4 transmitting a rotation from the input path T1 to the first element; a clutch C-3 transmitting the rotation from the input path T1 to the first second element C3; a brake B-1 engaging the fourth element; a brake B-2 engaging the second element, and an output member coupled with the third element R3.
Within the scope of DE 101 15 983 A1 by the Applicant, a multi-speed transmission is described comprising a drive shaft that is linked with a front-mounted gearset, an output shaft that is connected to a rear-mounted gearset, and a maximum of seven control elements, through the selective shifting of which at least seven forward gears can be shifted without range shifting. The front-mounted gearset is formed by a front-mounted planetary gearset or a maximum of two non-shiftable front-mounted planetary gearsets linked with the first front-mounted planetary gearset, wherein the rear-mounted gearset is configured as a two-carrier four-shaft transmission with two shiftable rear-mounted planetary gearsets and has four free shafts. The first free shaft of this two-carrier four-shaft transmission is linked with the first control element, the second free shaft with the second and third control elements, the third free shaft with the fourth and fifth control elements and the fourth free shaft is linked with the output shaft. According to the invention, a multi-step transmission with a total of six control elements is proposed, which connect the third free shaft or the first free shaft of the rear-mounted gearset additionally with a sixth control element. For a multi-step transmission with a total of seven control elements, according to the invention, it is proposed that the third free shaft is additionally connected to a sixth control element (D′) and the first free shaft additionally to a seventh control element.
The scope of DE 101 15 987 by the Applicant describes a multi-step transmission with at least seven gears. In addition to the input shaft and output shaft, this transmission comprises a non-engageable upstream gear and an engageable downstream gear in the form of a two-fixed-link four-shaft transmission. The upstream gear comprises a first planetary gearset, which in addition to the input rotational speed of the input shaft also provides a second rotational speed, which may optionally be shifted to the downstream gear. The downstream gear comprises two engageable planetary gearsets, which can shift at least seven gears using the six control elements, forming two power paths. During each shifting operation, range shifting is advantageously avoided. A 9-gear multi-speed transmission is furthermore known from DE 29 36 969. It comprises eight control elements and four gearsets.
Automatic vehicle transmissions in planetary design in general have previously been described in the state of the art on many occasions and undergo continuous development and improvements. These transmissions should have, for example, a sufficient number of forward gears as well as one reverse gear and a gear ratio that is excellently suited for motor vehicles, having a high overall spread as well as favorable progressive ratios. Furthermore, they should allow a high starting gear ratio in the forward direction and include a direct gear and additionally be suited for use both in passenger cars and in commercial vehicles. In addition, these transmissions should have a low complexity, in particular require a small number of control elements, and avoid double-shifts when shifting sequentially, so that only one control element is always engaged when shifting in defined gear groups.
Therefore, it is the object of the present invention to propose a multi-speed transmission of the type mentioned above in which the design complexity is optimized and furthermore the efficiency in the main driving gears with regard to drag and gearing losses is improved. Moreover, it is intended that low torque acts on the control elements and planetary gearsets in the multi-speed transmission according to the invention and that the rotational speeds of the shafts, control elements and planetary gearsets be kept as low as possible. In addition, the required number of gears and spread of the gear ratios should also be maintained, implementing advantageously six forward gears and at least one reverse gear. Furthermore, the transmission according to the invention should be suitable for any design in a vehicle, particularly for a frontal-transverse configuration.